Guide to Using the SegenSolar Battery Calculator You will be taken
Guide to Using the SegenSolar Battery Calculator
Perfect your battery sizing process with SegenSolar’s battery calculator tool. We know that every project involving
the use of battery storage is different: there is no ‘standard’ list of components that you can offer to a customer
because their needs will vary.
Sizing the battery capacity is dependent on many factors, and it is important to agree with the customer what the
proposed system will deliver in terms of functionality, capacity and compatibility.
SegenSolar’s Battery Storage Guide talks about how to go about these initial discussions with your customer:
agreeing what the daily demand is, and what they consider to be essential.
Once you have the all-important daily energy demand value, the SegenSolar Battery Calculator can be used to help
agree a suitable battery capacity with the customer.
From the SegenSolar portal home page, go to ‘Products’ and ‘Battery Calculator’.
You will be taken through to the calculator page. It’s intended to be a standalone tool, and won’t produce
a quote of parts at the end. It will help you decide what amount of battery capacity is appropriate, and
once you know that, you’re ready to either use the Design Tool, or speak to us about one of our storage
packages. You can find a complete list of the storage packages under ‘Products’ and PV Storage Products’.
Simply put, the tool will show what amount of PV yield is available from a given system, and compare the
hourly output with the hourly energy demands of the building. Whatever is left over is available to be
stored in a battery. It also shows how the battery state of charge (SOC) varies through the day and night,
based on the chosen load profile.
This document is a brief guide explaining how to complete the information field and how to interpret the
results and explain them to your customer.
Completing the site information section
Many of these fields are already defaulted based on your user profile. For example the Location information will
default to the address we have registered for you. Some of the other fields will need to be adjusted before results
can be produced. Here is an explanation of the fields.
This will default to your registered country.
This will default to your registered postcode, but you can change it to your customer’s site. Click
‘Find Address’ and there will be a short delay while the tool uses an online web server to look up the
PV yield data for that exact location. You will see the site coordinates update once it has successfully
found the data for the new location.
PV Array
Which way is the array facing? Azimuth means ideal (north facing). This field is asking how many
degrees off ideal the array faces. By default it will be set to 0, which means it is facing the azimuth. If
your system is facing east, you set it to -90, and west would be 90.
What angle will the PV array be at?
System Power This is what the rating of the PV array is in Watts. Eg 4kWp would be entered as 4000.
Unit Price
Monthly Cap
The cost of imported grid energy at the site. The currency and base value will default depending on
the country you’ve selected in the Location section.
If the site is on a tariff where the unit cost increases above a certain monthly usage, you can
add the higher unit rate and the point at which it’s applied.
Energy Usage
You need to select an energy usage profile. A load profile is how the daily energy consumption is
distributed throughout the 24 hour period. Every building and occupant is a bit different, and
therefore the pattern of energy usage will pretty much be unique. The main thing to be aware of is
whether there are people at home during the day or not. That will greatly affect how much of the PV
generated energy is available to be stored.
Energy Usage This is a daily total of energy consumption in Watt Hours (Wh). This is the value that will be modeled
using the Load Profile to work out what the hourly consumption is for the site. The tool will give you
a default usage value when you choose the load profile, but it’s important that the daily total is
something you’ve confirmed with your customer. It needs to be as accurate as possible.
You can add a reserve amount of capacity (in Wh) and the tool will set that amount of battery
capacity aside when it runs the calculations. It’s useful for certain sites that have energy demands
that must always be fulfilled, for example medical equipment. Especially useful if the grid supply is
Be aware, adding an energy reserve will effectively reduce the usage battery capacity for all the
other loads in the building. Also, the battery capacity will reduce over time but the reserve amount
will remain constant. It will therefore take up more and more of the usable capacity of the system.
You can toggle which parts of the results are displayed when the calculation is run. For example, you
could choose to hide the Costs section, and then the results would not include any of it. This could
be useful when discussing the results with your client.
Choose the type of battery to use in the calculation. The dropdown will show all the batteries we
have available.
How many batteries are to be used? In reality you can’t just have multiples of a battery: there will be
issues with communication and voltage, but this is intended to help you work out what battery
capacity is appropriate. Once you know that, you can decide on specific products as part of your
equipment design.
Battery capacity always decreases as time passes. When you are working out the most appropriate
battery capacity, you’ll want to make sure it can supply the necessary loads after some time has
passed, not just when it’s brand new. We would suggest running the calculation based on the
maximum year value to get more useful results.
When you have entered all the site information and design parameters, click Process or PDF
The Results section and how to interpret it
When you click Process, the tool will work for a moment and then display the results.
The first section is a summary of the battery capacity. The usable battery storage will be shown in year 1 and also for
the year you chose earlier. This is showing you how the usable capacity will reduce as time passes. The usable
capacity of a battery takes into account its available Depth of Discharge (DOD). In this example, a lead gel battery
rated at 8kWh has a DOD of 50%, so the usable energy capacity is 4kWh in year 1. By year 7, that capacity has
reduced to 2.4kWh.
If you entered a Reserve, you will notice that it will take up a greater proportion of the usable battery capacity as
time passes.
Here is a summary of what the results tables and charts show.
PV array yield
The results tables are all laid out in the same sort of format. You read the hours of the day from left to right, and the
different months top to bottom. The results from the whole year have been averaged to give a typical day for each
The first two table show what amount of PV yield is available for that site. Table A gives the yield per kWp of
installed power, and B shows the total available for the system size. For this site we have 1,687kWh/kWp and a
5kWp PV array, so the total annual yield will be about 8,400kWh.
The site energy consumption
The next two tables are normally read together. They show what energy the site is using every hour and what impact
the PV array is having on the amount of energy being drawn from the grid.
Table C shows the baseline energy consumption of the site over the 24 hour period. You will see the daily energy
total in Wh that you entered earlier. The load profile you chose has determined how that daily total is distributed
over 24 hours. In this example, the house is using 388.22Wh between 1am and 2am, and 672.93Wh between noon
and 1pm. If you keep the daily total consumption value the same but change the load profile selection, the values in
C will change to reflect the different pattern of energy usage.
Table D is overlaying the PV generation on top of the baseline consumption values. All the white boxes with negative
values are where energy is being drawn from the grid. We have a standard PV array here at the moment, so during
the night the values for each hour should match the baseline values in C. However, as the morning passes, the
amount of energy available from the PV will start to reduce the amount of energy required from the grid. When the
numbers become positive, it means there is a net excess of energy for that hour. The excess energy day peaks in the
middle of the day and then tails off again into the evening. The numbers will become negative and eventually match
the load profile base values again.
So what amount of energy is available to charge a battery?
The next two tables split the answer down to two views: firstly the excess energy from site, and then what is still
being drawn from the grid.
In Table E, the total amount of excess PV energy is shown in the Total column on the right, and Table F shows the
total daily energy consumption and the monthly cost. You can use these two tables to give your customer a
recommendation about whether it is worth adding battery storage to their site. If there is very little excess energy
left over once the energy demands have been taken into account, then there is little point adding storage. You might
also want to use these tables to show the energy savings that are possible with just PV.
Adding storage capacity
Now we see what happens when we add battery storage. Table G shows the battery state of charge (SOC) in Wh.
This is an indication of how full the battery is in each hour. The hours in each day when there is no battery charge
are shown with an ‘-‘. Looking at Table G, in the morning until 7am, there is no excess energy available so the battery
remains empty. As the supply starts to outstrip demand, the amount of stored energy increases until the battery is
full (at 2.4kWh). During the middle of the day the PV is producing more than the house can use, and so the battery
remains completely full. Then in the afternoon, as energy demand in the house becomes higher than the energy
from the PV, the battery SOC starts to drop until by about 9pm (or 8pm in winter) the battery is empty again.
Table H shows how the battery has impacted on the amount of imported energy and shows the new monthly cost on
the right.
These tables are showing you graphically what difference a given PV and storage capacity will make. You can
experiment with increasing the battery capacity or increasing the amount of PV energy. Here’s what happens to
Table G if we double the usable battery capacity.
Once again, the battery is fully charged in the middle of the day, but now there is stored energy available until late
into the evening, and all through until the next morning in summer. The household will still need to draw some
energy from the grid, but hugely less.
A completely off grid site obviously won’t be able to draw from the grid, but you could use Table G to identify when
a backup generator would need to be considered, or increase the battery capacity until there is energy available
Bear in mind that this is all based on averages: average PV production and average consumption and it is assuming
that the grid is always available to draw from. As long as you have an accurate daily value for the site and an idea of
the occupants’ pattern of usage, this is a very useful tool for making recommendations from.
Costs and Savings
Finally, a summary table represents these results in the form of costs and savings.
The leftmost columns show the baseline consumption and costs. These should hopefully be quite close to the actual
baseline data of the building. In reality energy usage (and therefore costs) will vary significantly throughout the year
and we are assuming pretty much constant consumption, but hopefully the annual total will be quite close. The most
important thing is the daily energy total. That’s what everything is based on.
The next column shows the monthly costs with a standard PV system (ie before storage). Since it’s based purely on
energy savings (ie not government incentives), it’s a very stable dataset to draw conclusions from.
The next four columns show the reduced costs and corresponding savings in year 1 and the final year of the battery
warranty period. You will notice here the annual savings by year 7 have reduced when compared to year 1.
The SegenSolar battery calculator is there as a guide to help you determine what battery capacity is appropriate for
a given site. It’s important that you know how much energy is needed for the site and what the pattern of usage is
(load profile).
The load profile you choose will show in Table C what amount of energy is assumed as being used for a given hour in
the calculation. If, in reality, the occupants decide to stay up all night with the TV on they will be deviating
significantly from the load profile and the battery system will be depleted faster than normal.
Table G also makes it very clear that using energy-hungry loads during the day is a good idea. Even when we
increased the battery capacity in our example it was still full in the middle of the day and any excess would be
wasted. Combine the introduction of PV and batteries with making the occupants aware of the importance of
managing their energy consumption and choosing the best time to use appliances.
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